Re: Why do we still perform a check for pre-sorted input within qsort variants?

I wrote:
> FWIW, I've been suspicious of that pre-sorted check since the day it
> went in. Bentley was my faculty adviser for awhile in grad school,
> and I know him to be *way* too smart to have missed anything as simple
> as that. But I didn't have hard evidence on which to object to it
> at the time, and indeed testing seemed to say it was a good idea:
> http://www.postgresql.org/message-id/18732.1142967137@sss.pgh.pa.us

BTW, after further review --- one thing that seems a little fishy is
that that test scaffolding made glibc's qsort look pretty good; which
was at variance with our previous experience, in which our version of
qsort seemed to dominate glibc's even before we took out the dubious
"swap_cnt" code, cf thread at
http://www.postgresql.org/message-id/Pine.LNX.4.58.0512121138080.18520@eon.cs
So there is definitely some room to argue that B&M's test scaffolding
doesn't match up with our real-world workloads. But before tinkering
too much with that code, it'd be good to understand why not, and to
have a test case we trust more.

regards, tom lane